Numerous applications of kinetic energy absorbers are known in the art. Examples include, but are not limited to, load attenuators for crash-resistant aircraft seats, spacecraft landing pods, crash-resistant aircraft landing gear, aircraft and vehicle passenger restraint harnesses, cargo tie-downs, automotive bumpers, collapsible vehicle steering columns and highway vehicle crash barriers and crash cushions. The common problem addressed in each of these applications is in the management and dissipation of excessive kinetic energy produced by high velocity moving bodies, during rapid deceleration of such bodies, in a safe and controlled manner so as to minimize injury to occupants or excessive damage to equipment and vehicles.
Energy attenuator devices typically rely on dissipating kinetic energy by plastic deformation of a solid object during impact loading. For example, devices which rely on energy absorption mechanisms such as bending wires or rods over bearing surfaces [see U.S. Pat. No. 3,087,584 to Jackson, et al.; U.S. Pat. No. 3,195,685 to Blackstone; U.S. Pat. No. 3,968,863 to Reilly], axial compression and buckling of metal tubes [see U.S. Pat. No. 2,870,871 to Stevinson; U.S. Pat. No. 3,146,014 to Kroell], axial compression and rupturing of tubes [See U.S. Pat. No. 3,143,321 to McGehee, et al.; U.S. Pat. No. 3,236,333 to Mitchell; U.S. Pat. No. 5,074,391 to Rosenzweig; U.S. Pat. No. 6,308,809 to Reid et al.], lateral compression of tubes [see U.S. Pat. No. 3,719,255 to Daniels, et al.; U.S. Pat. No. 4,200,310 to Carney; U.S. Pat. No. 4,289,419 to Young, et al.; U.S. Pat. No. 6,082,926 to Zimmer], diametric crimping of tubes [see U.S. Pat. No. 3,820,634 to Poe; U.S. Pat. No. 4,223,763 to Duclos, et al.], and bending metal strips or straps over rollers or shaped surfaces [see U.S. Pat. No. 2,578,903 to Smith; U.S. Pat. No. 2,979,163 to Van Zelm, et al.; U.S. Pat. No. 2,980,213 to Van Zelm, et al.; U.S. Pat. No. 3,017,163 to Van Zelm, et al.; U.S. Pat. No. 3,211,260 to Jackson; U.S. Pat. No. 3,337,004 to Hoffman, et al.; U.S. Pat. No. 3,547,468 to Giuffrida; U.S. Pat. No. 3,561,690 to Muskat; U.S. Pat. No. 3,730,586 to Eggert; U.S. Pat. No. 4,027,905 to Shimogawa, et al.; U.S. Pat. No. 4,358,136 to Tsuge, et al.; U.S. Pat. No. 4,630,716 to Faust] are known in the art.
Irrespective of the deformation method employed, these prior art energy dissipation devices are generally designed to operate at a constant force and to dissipate a fixed amount of energy. As such, due to designed limitations in energy absorption capacity and deceleration force, these prior art devices are typically unsuitable for handling a wide range of impact masses, velocities or kinetic energies. Furthermore, while these prior art devices may effectively dissipate the kinetic energies for which they are designed, due to their typical constant force limitations, they generally do not provide for effective management and control of harmful deceleration forces produced by varying force-time profiles. Additionally, since these prior art devices typically rely on kinetic energy dissipation through the irreversible plastic deformation of deforming members at stresses well above their proportional limit and yield point, such devices are inherently inefficient in extracting deformation energy from materials since, following initial deformation of the members, subsequent deformation and energy dissipation is minimal since the initial deformation is typically irreversible. Furthermore, these devices have associated high maintenance costs since, deforming members must be replaced after use due to irreversible deformation.
A particularly beneficial example application of energy dissipater devices is in highway crash barriers designed to protect vehicles and occupants from collision damage or injury from high velocity impact with fixed roadside objects. U.S. Pat. No. 4,844,213 to Travis discloses a progressively collapsing barrier where frictional sliding of a securing member along a track permits the collapsing components to move together. U.S. Pat. No. 5,634,738 to Jackson, et al. discloses a restraining vehicle barrier for railroad crossings which employs an energy absorbing metal cable or strip spool payout mechanism wherein energy is absorbed by bending and deformation of the strip in multiple steps. The metal strip spools are replaced after use. The disclosed device permits vehicles to be stopped within about 30 yards. U.S. Pat. No. 5,391,016 to Ivey, et al. discloses a collapsible telescoping highway guardrail terminal for attenuating head-on vehicle impacts. U.S. Pat. No. 5,791,812 to Ivey discloses a collapsible guardrail end treatment for preventing penetration of vehicles by guardrail ends during head-on or side-impact collisions. U.S. Pat. No. 6,179,516 to Ivey, et al. discloses a collapsible highway divider end treatment comprising a sliding frame and crushable barrels for absorbing vehicle impact energy and redirecting impacting vehicles. The disclosed device provides a relatively constant crush resistance.
In addition to the above examples, numerous other energy absorbing highway crash barriers are known in the art including, but not limited to break away cable terminals or BCTs [see FHWA Technical Advisory T 5040.25], eccentric loader breakaway cable guardrail terminals or ELTs [see FHWA Technical Advisory T 5040.25], modified eccentric loader breakaway cable terminals or MELTs [see Federal Motor Vehicle Safety Standards, Technical Report 208, National Highway Traffic Safety Administration, Washington, D.C. 1971], enhanced MELTs for side-impact or MELT-SIs [see M. H. Ray, et al., “Side Impact Crash Testing”, Federal Highway Administration Report No. FHWA-RD-92-052, March 1992] guardrail extruder terminals such as the ET-2000 [see U.S. Pat. No. 4,928,928 to Buth et al. and U.S. Pat. No. 5,078,366 to Sicking et al.], slotted rail terminals (SRTs} and vehicle attenuating terminals or VATs.
One particularly promising application for a variable force energy dissipater is as a highway crash cushion to protect vehicle occupants during side impacts with a fixed roadside object. In a series of three reports which reviewed the 1983 Fatal Accident Reporting System (FARS) and the 1985 National Accident Sampling System (NASS) databases maintained by the National Highway Traffic Safety Administration (NHTSA), Ray, et al., investigated the causes and severity of side impact collisions with fixed roadside objects such as trees, utility poles and guardrails and reported that 25% of major accidents can be attributed to side impact collisions of a single vehicle with a fixed roadside object. Observed impact velocities were typically 50 km/hr and impact angles were typically around 90° [see M. H. Ray, et al., Federal High Administration Report No. FHWA-RD-91-122, FHWA-RD-92-062 and FHWA-RD-92-079]. Based on their data analysis Ray, et al., identified typical vehicle speed, impact location and vehicle orientation characteristics for reported side impact collisions [see M. H. Ray, et. al., “Characteristics of Side Impact Accidents involving Fixed Roadside Objects”, ASCE Journal of Transportation, Vol. 117, No. 3, May/June 1991; L. A. Troxel, et al., “Side Impact Collisions with Roadside Objects”, Roadside Safety Features, Transportation Research Record No. 1302, Transportation Research Board, 1991].
From their analysis of FARS and NASS accident data, Ray, et al. provided recommendations for performing and evaluating side impact crash test performance of roadside structures and associated occupant risks by evaluating side impact crashes of small 820 kg vehicles, at impact angles of 90° and impact velocities of 50 km/hr [see M. H. Ray, et al., Federal High Administration Report No. FHWA-RD-92-062]. In subsequent testing, Ray, et al., evaluated the performance of conventional highway crash guardrail terminals in side impact collisions and found that existing devices failed to protect vehicle occupants from significant intrusion of guardrail terminals into passenger compartments which is a major source of fatal injuries in side impact collisions [see M. H. Ray, et al., Report Nos. FHWA-RD-92-047, FHWA-RD-92-048, FHWA-RD-92-051 and FHWA-RD-92-052, Federal Highway Administration, Washington, D.C., March 1992].
In a subsequent report, Ray, et al., conducted side impact testing of conventional roadside structures and developed preliminary statistical models to evaluate the risk of occupants [see M. H. Ray, et al., Federal High Administration Report No. FHWA-RD-92-079; Ray, et al., “Severity Measure in Side-Impacts with Narrow Roadside Structures”, J. Trans. Eng. 120(2):322-338 (March/April 1994)]. Based on an analysis of reported side-impact accidents involving fixed roadside objects, Ray, et al. proposed road test criteria and crash evaluation methods for evaluating highway guardrail and crash cushion performance [see Ray, et al., “Test and Evaluation Criteria for Side-Impact Roadside Appurtenance Collisions”, J. Trans. Eng. 120(4):633-651 (July/August 1994); Ray, et al., “Side Impact Crash Test and Evaluation Criteria for Roadside Safety Hardware”, in General Design and Roadside Safety Features, Transportation Research Record No. 1647, Transportation Research Board (Washington, D.C. 1999); Ray, et al., “Impact Conditions in Side Impact Collisions with Fixed Roadside Objects”, in Accident Analysis and Prevention, vol. 31, no. 1 (Pergamon Press 1999)].
For the purpose of assessing guardrail and crash cushion performance and predicting occupant injury risks for roadside barriers in side-impact collisions, a refined analysis for evaluation of occupant injury risks and a Side-Impact Occupant Impact Velocity (SI-OIV) evaluation criterion was provided by Ray, et al. for side impact collisions based on the difference in impact velocities of vehicles and occupants upon initial impact with fixed roadside objects. In a series of full-scale side impact tests, Ray, et al. examined conventional experimental measurements made with Anthropomorphic Test Devices (ATD) or “crash dummies” and refined the SI-OIV method for predicting severity of occupant head, thoracic and pelvic injuries [see Ray, et al., “Evaluating Human Risk in Side Impact Collisions with Roadside Objects”, Transportation Research Record No. 1720, Transportation Research Board (Washington, D.C. 2000); M. H. Ray, “Side Impact Test and Evaluation Procedures”, Federal High Administration Report No. FHWA-RD-00-XXX, Contract No. DFH61-96-R-00068, Final Report Fall 2001].
Based on a review of recent studies of side impact collisions and resultant occupant injuries, Ray, et al. concluded that conventional crash cushions and guardrails are primarily designed for dissipating vehicle kinetic energy in head-on collisions and are not adequately designed to minimize occupant injury during side-impact collisions with their associated acceleration profiles [see M. H. Ray, “Side Impact Test and Evaluation Procedures”, Federal High Administration Report No. FHWA-RD-00-XXX, Contract No. DFH61-96-R-00068, Final Report Fall 2001]. While conventional roadside crash cushions and guardrails are typically designed to produce a constant deceleration force for absorbing vehicle kinetic energy, Ray, et al. demonstrated that variable force crash cushions are required to minimize injuries to occupants caused by impact with vehicle interiors during side-impact collisions. In addition, Ray, et al. demonstrated that decelerations produced by current generation crash cushions are suitable for either small 820 kg passenger cars or large 2000 kg pickup trucks but are not appropriate for the majority of 1450 kg mid-sized vehicles.
For all of the above reasons, a variable force energy dissipater would be particularly desirable for use in highway crash cushions during both frontal and side impacts so as to minimize the deceleration forces that vehicle occupants are exposed to, provide for a wide variety of vehicle weights and speeds, and provide for force adjustments to match anticipated impact conditions so as to avoid severe injuries to vehicle occupants caused by excessive deceleration forces.
Additionally, in light of the limitations of existing energy dissipater devices, it would be particularly advantageous to provide an energy attenuating which provides for varying the resistance force during impact and which dissipates a broad range of kinetic energy in anticipation of a variety of load impact scenarios involving wide ranges in mass, velocity or kinetic energy. Such a device would permit effective management and control over harmful deceleration forces produced by different force-time impact profiles, for example different sized vehicles. Furthermore, by relying on kinetic energy dissipation through reversible deformation of deforming members below their failure point, such a device would be inherently efficient in extracting maximum deformation energy from viscoelastic materials where successive deformation of the members may be continually repeated due to the reversible nature and subsequent recovery of initial viscoelastic deformation.